In some cases, the cells might need to be manipulated before being used as a treatment, said Dr Gerald Schatten, from the University of Pittsburgh, US, who worked with the Seoul National University team.

Researchers will also need to develop ways to efficiently direct the growth of stem cells into stable cell types, said Professor Woo Suk Hwang and his colleagues who successfully cloned human embryos last year.

"Scientists must also find a way to remove the remaining animal components from the laboratory procedures," they said.

Currently, scientists use animal enzymes to isolate the cells needed for such research.

They also stressed that the technique should not be used to make genetically identical babies - called reproductive cloning.

The technique.

Stem cells are primitive "master" cells that can be programmed to become many kinds of tissue.

To make them patient-specific, the researchers took DNA from the skin cells of volunteers and put this genetic material into donated human eggs which had had their own genetic material removed.

These eggs were grown to a very early stage of embryo development, around six days, when they were still just small balls of cells. The scientists then extracted the stem cells.

Cloning for research purposes is profoundly unethical.

Julia Millington of the ProLife Alliance

When the researchers examined them in the laboratory, the stem cells appeared to be immunologically compatible to the individual who donated the DNA.

Professor Chris Higgins, from the UK Medical Research Council, said: "It really is an advance. It offers the possibility of stem cell therapies without rejection.

"Also, the scientists have improved their technique and reliability of stem cell transfer."

Professor Ian Wilmut, from the Roslin Institute in Edinburgh and creator of Dolly the sheep, said: "These new observations make a very significant and important step forward toward the use of cells from cloned human embryos for research and therapy."

Roger Pedersen, Professor of Regenerative Medicine, University of Cambridge, said the work provided "ample evidence" for the feasibility of replacing the genome of a human egg with that of an adult body cell.

Story from BBC NEWS: http://news.bbc.co.uk/go/pr/fr/-/1/hi/health/4555023.stm